1. Field of the Invention
The present invention relates to a preignition detection apparatus for an internal combustion engine, and more particularly to a preignition detection apparatus capable of detecting a preignition condition in an incipient stage.
2. Prior Art
Preignition is defined as the phenomenon that an air-fuel mixture is spontaneously ignited during the compression stroke by residual heat contained in deposits which adhere to the ignition plug and/or an inner wall of an engine cylinder.
Preignition causes not only a sharp decrease of the output of an engine and/or a fluctuation of engine speed, but can also damage the engine, at the worst.
To solve this problem, there has already been proposed an internal combustion engine control device which determines that preignition has occurred when abnormal engine vibration, a magnitude thereof being greater than a predetermined level, is detected before ignition, and cuts off fuel to the cylinder (See Japanese Utility Model Publication No. 1-88052).
The above-mentioned engine control device, however, cannot prevent the engine being damaged, because it determines that preignition has occurred when abnormal engine vibration, the magnitude thereof being greater than a predetermined level, is detected and cannot determine that preignition has occurred until after preignition has become significantly serious.